The present invention generally relates to a motor having a hydrodynamic bearing, and more particularly to a cooling device using the motor for efficiently cooling e.g. semiconductor devices.
FIG. 7 is a cross section depicting a structure of a conventional cooling device employing a motor having a hydrodynamic bearing. FIG. 8 is a cross section of a motor-bearing employed in the cooling device of FIG. 7.
A structure of the prior art is described hereinafter with reference to FIG. 7 and FIG. 8.
Housing 141 having one open side and a cup-shape is protrusively formed on a recess of frame 101. Housing 141 secures stator 103 on its outer wall, and stator 103 is wound with coil 102. Driving circuit substrate 104 is disposed around housing 141. Substrate 104 holds stator 103 and connects electrically a terminal of coil 102 to a wiring formed on substrate 104 by soldering. Substrate 104 is equipped with electronic components constituting the driving circuit and Hall elements. Insulating sheet 120 is disposed between substrate 104 and frame 101.
Frame 101 is surrounded by a side wall and has an upward opening. Bell-mouth 119 is disposed around the opening to promote airflow. Housing 141 fixedly secures thrust plate 106 and thrust sheet 107 on its bottom face. Sleeve 105 is fit into housing 141. Stator unit 115 comprises these elements discussed above, i.e. frame 101, housing 141, sleeve 105, coil 102 and stator 103.
Rotary shaft 109 extends through sleeve 105 and is axially supported by thrust plate 106 as well as rotatably supported by sleeve 105. Fan 108 is mounted to shaft 109. Washer 110 fixed on shaft 109 prevents fan 108 from coming off from sleeve 105. Magnet 111 is bonded to fan 108 via magnet yoke 112 so that magnet 111 faces stator 103. Rotor 116 comprises the elements discussed above, i.e. magnet 111, yoke 112 and fan 108.
The bearing of the motor is detailed hereinafter with reference to FIG. 8.
In FIG. 8, sleeve 105 is equipped with oil reservoir 147 in the center portion of its inner wall. Oil reservoir 147 has a greater inner diameter than other parts of the inner wall of sleeve 105. Sleeve 105 has dynamic-pressure-generating grooves 113. Grooves 113 are formed by a ball-rolling-process. Oil 114 is provided to grooves 113 as lubricant for sleeve 105 and shaft 109. Radial bearing 117 is thus formed as discussed above.
The tip of shaft 109 facing thrust plate 106 is finished into a spherical face that contacts thrust sheet 107 so that thrust plate 106 and thrust sheet 107 support shaft 109 axially. Thrust bearing 118 is thus structured as discussed above.
The conventional motor employing this hydrodynamic bearing, however, has the following problems.
In recent years, electronics apparatuses have been obliged to generate a greater amount of heat in order to satisfy market demands such as higher performance as well as down sizing. This situation forces the cooling devices and the cooling-fan-motors of those apparatuses to encounter greater changes in temperatures, and requires them to increase their cooling performance.
In the conventional motor, first, stopper washer 110 is mounted to shaft 109 in order to prevent fan 108 from coming off from the bearing, then thrust sheet 107 and thrust plate 106 are fixedly press-fitted into frame 101. Therefore, temperature change cycles produce a gap between thrust plate 106 and frame 101, and thus oil 114 spills from the gap.
Since thrust plate 106 is independent of frame 101, the flatness of the bottom face of frame 101 is difficult to improve, which reduces adherence between this cooling device and a heating element 300. Further, the center portion, which produces a greater amount of heat than other portions of the heating element, or a device attached to this heating device, can not be substantially cooled down.
The cooling device requires a higher rotational speed in order to increase the cooling performance, which also increases centrifugal forces produced by shaft 109 and fan 108. Oil 114 in the bearing thus flows out along shaft 109 and fan 108, which entails the outflow of oil 114 from dynamic-pressure-generating groove 113. This out-flow causes an oil shortage, which lowers the number of rotations and produces locking of rotor 116.
Further, the downsizing of motors narrows the space for the bearing, miniaturizes the components, and increases the number of components of motors. Thus fabrication of the motor requires more complicated work.
The present invention addresses the problems discussed above, and aims to provide a motor free from oil-spill from its bearing due to temperature change cycles or motor rotation, and also provides a cooling device using the motor for achieving efficient cooling.
The motor of the present invention comprises the following elements:
(a) a frame having an opening;
(b) a frame-housing provided on the unitary frame and having one side thereof open;
(c) a stator secured on an outer wall of the frame-housing;
(d) a sleeve fit into the frame-housing;
(e) a thrust supporter provided on a unitary bottom face of the frame housing;
(f) a shaft supported by the thrust supporter at the end thereof, inserted into the sleeve, and rotatably supported by the sleeve;
(g) a rotor securing the shaft;
(h) a magnet disposed on the rotor and opposite to the stator; and
(i) oil provided in the space between the shaft and sleeve.
The construction discussed above saves the fitted section of the frame and thrust supporter, because the thrust supporter is unitarily formed with the bottom face of the frame housing. The oil-spill due to the temperature change cycles can thus be avoided, and as a result, the reliability and life-span of the motor can be increased.
The unitary forming of the thrust supporter with the bottom face of the frame-housing can improve the flatness of the bottom face, whereby the adherence between the bottom face and the heating element is improved. The heat conductivity from the heating element to the frame can thus be improved. As a result, the cooling performance of the cooling device can be boosted.
In another motor of the present invention, a rib is formed on the rotor rim within which the shaft is mounted, thereby blocking the oil splashed from the space between the shaft and sleeve. As a result, the oil can be prevented from flowing out from the bearing when the motor is in operation.
The cooling device of the present invention comprises the following elements:
(a) a frame having a first opening on a first face surrounded by a side wall and being mountable with a heating element on a second face;
(b) a frame-housing formed on the frame and having one side thereof open;
(c) a stator secured on an outer wall of the housing;
(d) a sleeve fit into the frame-housing;
(e) a thrust supporter unitarily formed with a bottom face of the frame-housing;
(f) a shaft supported by the thrust supporter at the end of the shaft, inserted into the sleeve, and rotatably supported by the sleeve;
(g) a rotor securing the shaft;
(h) a magnet disposed on the rotor and opposite to the stator;
(i) oil provided in the space between the shaft and sleeve;
(j) second openings provided on the side wall of the frame; and
(k) a fan provided on the rotor.
The construction discussed above saves the fitted section of the frame and thrust supporter, because the thrust supporter is unitarily formed with the bottom face of the frame housing. The oil-spill due to the temperature change cycles can thus be avoided, and as a result, the reliability and life-span of the motor can be increased.
The unitary formation of thrust supporter with the bottom face of frame-housing can improve the flatness of the bottom face, whereby the adherence between the bottom face and the heating element is improved. The heat conductivity from the heating element to the frame can thus be improved. As a result, the cooling performance of the cooling device can be boosted.
The cooling device draws air from the first opening by rotating the fan, and discharges the air through the second openings. The airflow produced by the draw and discharge operations travels on the frame so that the heat within the frame can be efficiently dissipated. The locations, sizes, and numbers of the second openings can be adaptively determined so that the airflow discharged from the second openings can be blown on the other heating elements or can discharge heated air in a smooth manner. As a result, a cooling device of high performance can be achieved.